The present invention relates to a clock-generating circuit and an image-forming apparatus employing fxcex8 lens in an optical writing section, and specifically relates to a combination of an image-forming apparatus and a clock-generating circuit, which makes it possible to reduce influence to the image quality caused by property errors of the fxcex8 lens.
In conventional image-forming apparatus, an image is formed on an image-bearing member rotating in a sub-scanning direction by scanning a laser beam, modulated in response to image data, in a main-scanning direction. In this operation, the laser beam is modulated in response to the image data in reference to reference signals called as dot clock pulses.
Incidentally, FIG. 7 shows perspective view of a configuration of the optical writing section employing a laser beam in the image-forming apparatus as described in the above. As shown in FIG. 7, laser diode 470 (LD) emits the laser beam based on the laser driving signals generated by circuit section 400.
Further, the laser beam, emitted by laser diode 470 and having been passed through collimator lens 491 and cylindrical lens 492, is deflected for scanning by polygon mirror 493, and scans image-bearing member 1 for writing, after passing through fxcex8 lens 494 so as to adjust the scanning velocity at constant and cylindrical lens 495. In addition, a part of the laser beam deflected by polygon mirror 493 is led to index sensor 412 for detecting the timing.
First Problem
In case of the image-forming apparatus, which employs the laser beam as writing means, the expansion of the casing mainframe caused by increase of its temperature influences various kinds of optical elements. For instance, a certain optical property would be varied by the change of a length between lenses.
Further, since general fxcex8 lenses are made of plastic material with mold by employing the plastic molding process, refractive indexes of them are apt to vary with the change of ambient temperature. When the ambient temperature changes under the normal operating conditions of the apparatus, fxcex8 property change (fxcex8 property error) of around xc2x10.8% (a uniformity of scanning velocity of the laser beam on the surface of the image-bearing member) would occur as shown in FIG. 8.
Second Problem
To attain the fxcex8 property, which sufficiently makes the scanning velocity of the laser beam on the surface of image-bearing member uniform, fxcex8 lens should be shape in a complicated spherical or aspherical lens. It is impossible, however, to design such fxcex8 lens that has completely no fxcex8 property error. Accordingly, fxcex8 property error of around xc2x10.1% still remains even in the design stage of fxcex8 lens, as shown in FIG. 9.
Further, since the fxcex8 property error has dependability on wavelength of the laser beam, the fxcex8 property is attained by reducing various kinds of aberrations at a predetermined wavelength of the laser beam. Accordingly, since the wavelengths of the laser beams emitted by laser diodes of the same kind would slightly vary relative to each other due to the slight differences between individualities of the laser diodes, the deviation from the predetermined wavelength in each of the laser diodes would result in the fxcex8 property error. In order to strictly control the wavelengths of the laser beams emitted by laser diodes, however, it is necessary to select usable laser diodes out of a large amount of laser diodes, resulting in increase of the production cost of the apparatus concerned, which has been one of problems. For instance, in a color image-forming apparatus, which provides four stages of image-writing units corresponding to four primary colors, there happens a problem that images corresponding to four primary colors deviate relative to each other due to occurrence of the fxcex8 property error in each of the four image-writing units, unless the wavelengths of the laser beams, emitted by the laser diodes employed in the four image-writing units, are completely coincided each other.
Third Problem
When the fxcex8 lenses are manufactured through the plastic molding process, which employs molds, refractive indexes of the manufactured fxcex8 lenses vary with the variations of the molds. The molds would vary one by one, when the fxcex8 lenses are simultaneously manufactured in parallel by employing a plurality of molds, or when an old mold is replaced by a new mold every predetermined period of time, etc. Generally speaking, as shown in FIG. 10, a variation between molds would result in fxcex8 property change (fxcex8 property error) of around xc2x10.1% (a uniformity of scanning velocity of the laser beam on the surface of the image-bearing member). In order to suppress the fxcex8 property error, the variations between the molds should be strictly controlled, resulting in increase of manufacturing cost of the molds as well as increase of the production cost of the apparatus concerned, which has been another one of problems.
Forth Problem
In the fxcex8 lens-manufacturing site, sometimes, variations of refractive indexes of the fxcex8 lenses are caused by the variations of manufacturing processes corresponding to differences of manufacturing dates of them, etc. In order to suppress the fxcex8 property error, the variations between the manufacturing processes should be strictly controlled, resulting in increase of manufacturing cost of the fxcex8 lens as well as increase of the production cost of the apparatus concerned, which has been another one of problems.
To overcome the abovementioned drawbacks in conventional image-forming apparatus, it is an object of the present invention to provide a clock-generating circuit and an image-forming apparatus employing the polygon mirror as writing means, which make it possible to reduce the influence to the image quality, caused by the fxcex8 property error.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by clock-generating circuits and image-forming apparatus described as follow.
(1) A circuit for generating dot clock pulses for driving a light-emitting element employed in an optical-writing section of an image-forming apparatus, comprising: a digital-delay dot clock adjusting section to adjust timings of rising-edges or falling-edges of the dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; and a controlling section to control a selecting operation for the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting section, so as to compensate for a fxcex8 property error of a fxcex8 lens employed in the optical-writing section.
(2) A circuit for generating dot clock pulses for driving a light-emitting element employed in an optical-writing section of an image-forming apparatus, comprising: an index sensor to detect a light-beam, which is emitted from the light-emitting element and is deflected for scanning by a light-scanning device employed in the optical-writing section, and to output an index signal when the index sensor detects the light-beam at an end portion of a main-scanning region scanned by the light-beam; a delay-chain section to generate a plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; a synchronized clock pulse detecting section to select synchronized delayed-clock pulses, which are synchronized with the index signal, out of the plurality of delayed clock pulses generated in the delay-chain section, and to output a number of delay-stages, which is derived from the synchronized delayed-clock pulses, as synchronizing information; a table memory to store fxcex8 property error information, which represents a fxcex8 property error of a fxcex8 lens employed in the optical-writing section; a delayed-clock switching section to generate a select signal, for selecting a specific delayed-clock pulse, having a phase suitable for compensating for the fxcex8 property error of the fxcex8 lens employed in the optical-writing section, out of the plurality of delayed-clock pulses, based on the synchronized delayed-clock pulses and the synchronizing information outputted from the synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory; and a selector to select the specific delayed-clock pulse out of the plurality of delayed-clock pulses in response to the select signal generated by the delayed-clock switching section.
(3) The circuit of item 2, wherein the select signal is generated in the delayed-clock switching section by performing a calculating operation, based on the synchronized delayed-clock pulses outputted by the synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory.
(4) The circuit of item 2, wherein the select signal is generated in the delayed-clock switching section by performing a table-converting operation, based on the synchronized delayed-clock pulses outputted by synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory.
(5) The circuit of item 2, wherein the fxcex8 property error is caused by a variation of refractive index of the fxcex8 lens due to an ambient temperature change.
(6) The circuit of item 2, wherein the fxcex8 property error is a deviation from an ideal value established as a fxcex8 lens design value.
(7) The circuit of item 2, wherein the fxcex8 property error is caused by an inaccuracy of a mold for molding the fxcex8 lens.
(8) The circuit of item 2, wherein the delay-chain section, the synchronized clock pulse detecting section, the table memory and the selector are digital circuits fabricated in an integrated circuit.
(9) An image-forming apparatus, comprising: an image-forming section that includes an optical-writing section to form an image; and a circuit for generating dot clock pulses for driving a light-emitting element employed in the optical-writing section included in the image-forming section; wherein the circuit includes, a digital-delay dot clock adjusting section to adjust timings of rising-edges or falling-edges of the dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times, and a controlling section to control a selecting operation for the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting section, so as to compensate for a fxcex8 property error of a fxcex8 lens employed in the optical-writing section; and wherein the image-forming section performs an image-forming operation based on clock signals outputted from the digital-delay dot clock adjusting section.
(10) An image-forming apparatus, comprising: an image-forming section that includes an optical-writing section to form an image; and a circuit for generating dot clock pulses for driving a light-emitting element employed in the optical-writing section included in the image-forming section; wherein the circuit includes: an index sensor to detect a light-beam, which is emitted from the light-emitting element and is deflected for scanning by a light-scanning device employed in the optical-writing section, and to output an index signal when the index sensor detects the light-beam at an end portion of a main-scanning region scanned by the light-beam; a delay-chain section to generate a plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; a synchronized clock pulse detecting section to select synchronized delayed-clock pulses, which are synchronized with the index signal, out of the plurality of delayed clock pulses generated in the delay-chain section, and to output a number of delay-stages, which is derived from the synchronized delayed-clock pulses, as synchronizing information; a table memory to store fxcex8 property error information, which represents a fxcex8 property error of a fxcex8 lens employed in the optical-writing section; a delayed-clock switching section to generate a select signal, for selecting a specific delayed-clock pulse, having a phase suitable for compensating for the fxcex8 property error of the fxcex8 lens employed in the optical-writing section, out of the plurality of delayed-clock pulses, based on the synchronized delayed-clock pulses and the synchronizing information outputted from the synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory; and a selector to select the specific delayed-clock pulse out of the plurality of delayed-clock pulses in response to the select signal generated by the delayed-clock switching section; and wherein the image-forming section performs an image-forming operation based on clock signals outputted from the selector.
(11) The image-forming apparatus of item 10, wherein the select signal is generated in the delayed-clock switching section by performing a calculating operation, based on the synchronized delayed-clock pulses outputted by the synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory.
(12) The image-forming apparatus of item 10, wherein the select signal is generated in the delayed-clock switching section by performing a table-converting operation, based on the synchronized delayed-clock pulses outputted by synchronized clock pulse detecting section and the fxcex8 property error information stored in the table memory.
(13) The image-forming apparatus of item 10, wherein the fxcex8 property error is caused by a variation of refractive index of the fxcex8 lens due to an ambient temperature change.
(14) The image-forming apparatus of item 10, wherein the fxcex8 property error is a deviation from an ideal value established as a fxcex8 lens design value.
(15) The image-forming apparatus of item 10, wherein the fxcex8 property error is caused by an inaccuracy of a mold for molding the fxcex8 lens.
(16) The image-forming apparatus of item 10, wherein the delay-chain section, the synchronized clock pulse detecting section, the table memory and the selector are digital circuits fabricated in an integrated circuit.
Further, to overcome the abovementioned problems, other clock-generating circuits and image-forming apparatus, embodied in the present invention, will be described as follow:
(17) A clock-generating circuit characterized by comprising:
digital-delay dot clock adjusting means for changing timings of rising-edges or falling-edges of dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; and
controlling means for controlling a selection of the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting means, so as to compensate for a fxcex8 property error of a fxcex8 lens employed in a writing section.
(18) An image-forming apparatus characterized by comprising:
digital-delay dot clock adjusting means for changing timings of rising-edges or falling-edges of dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times;
controlling means for controlling a selection of the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting means, so as to compensate for a fxcex8 property error of a fxcex8 lens employed in a writing section; and
image-forming means for performing image-forming operations based on clock signals from the digital-delay dot clock adjusting means.
According to the above invention, since a plurality of delayed-clock pulses are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times, and a selection of the plurality of delayed clock pulses is changed in response to scanning unevenness of a polygon mirror, it is possible to cancel the fxcex8 property error of a fxcex8 lens on the surface of the image-bearing member by slightly changing timings of rising-edges or falling-edges of dot clock pulses.
As a result, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens, with a simple circuit configuration.
(19) A clock-generating circuit characterized by comprising:
a delay-chain section to generate a plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times,
a synchronized clock pulse detecting section to select a plurality of delayed-clock pulses (synchronized delayed-clock pulses), which are synchronized with an index signal being a reference of an end portion, from the delay-chain section, and to output a number of delay-stages of the delay-chain section from the synchronized delayed-clock pulses, as synchronizing information;
a table to hold fxcex8 property error information, pertaining to a fxcex8 property error of a fxcex8 lens used in the writing section;
a synchronized switching section to generate a select signal, for determining what phased delayed-clock pulse should be selected out of the plurality of delayed-clock pulses from the synchronized delayed-clock pulses and the synchronizing information outputted from the synchronized clock pulse detecting section and the fxcex8 property error information from the table; and
a signal selecting section to select the delayed-clock pulse corresponding to the select signal out of the plurality of delayed-clock pulses.
(20) An image-forming apparatus characterized by comprising:
a delay-chain section to generate a plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times,
a synchronized clock pulse detecting section to select a plurality of delayed-clock pulses (synchronized delayed-clock pulses), which are synchronized with an index signal being a reference of an end portion, from the delay-chain section, and to output a number of delay-stages of the delay-chain section from the synchronized delayed-clock pulses, as synchronizing information;
a table to hold fxcex8 property error information, pertaining to a fxcex8 property error of a fxcex8 lens used in the writing section;
a synchronized switching section to generate a select signal, for determining what phased delayed-clock pulse should be selected out of the plurality of delayed-clock pulses from the synchronized delayed-clock pulses and the synchronizing information from the synchronized clock pulse detecting section and the fxcex8 property error information from the table;
a signal selecting section to select the delayed-clock pulse corresponding to the select signal out of the plurality of delayed-clock pulses; and
image-forming means for performing an image-forming operation based on the clock signals outputted from the signal selecting section.
According to the above invention, since the delay-chain section generates the plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times, and the selection of the plurality of delayed-clock pulses in the signal selecting section is changed by the select signal from the synchronized clock pulse detecting section based on the synchronizing information from the synchronized clock pulse detecting section and the fxcex8 property error information held in the table, it is possible to cancel the fxcex8 property error of the fxcex8 lens on the surface of the image-bearing member by slightly changing timings of rising-edges or falling-edges of dot clock pulses.
As a result, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens, with a simple circuit configuration.
(21) The clock-generating circuit described in item 19, characterized in that synchronized switching section generates the select signal by performing a calculating operation, from the synchronized delayed-clock pulses from the synchronized clock pulse detecting section and the fxcex8 property error information from the table.
(22) The image-forming apparatus described in item 20, characterized in that synchronized switching section generates the select signal by performing a calculating operation, from the synchronized delayed-clock pulses from the synchronized clock pulse detecting section and the fxcex8 property error information from the table.
According to the above invention, since a plurality of delayed-clock pulses are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times, and the selection of the plurality of delayed-clock pulses is changed in response to the result of calculations performed by referring to the fxcex8 property error of the fxcex8 lens, it is possible to cancel the fxcex8 property error of the fxcex8 lens on the surface of the image-bearing member by slightly changing timings of rising-edges or falling-edges of dot clock pulses.
As a result, in the image-forming apparatus incorporating a polygon mirror in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens, with a simple circuit configuration.
(23) The clock-generating circuit described in item 19, characterized in that synchronized switching section generates the select signal by performing a table-converting operation, from the synchronized delayed-clock pulses from the synchronized clock pulse detecting section and the fxcex8 property error information from the table.
(24) The image-forming apparatus described in item 20, characterized in that synchronized switching section generates the select signal by performing a table-converting operation, from the synchronized delayed-clock pulses from the synchronized clock pulse detecting section and the fxcex8 property error information from the table.
According to the above invention, since a plurality of delayed-clock pulses are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times, and the selection of the plurality of delayed-clock pulses is changed in response to the result of a table-converting operation performed by using a look-up table while referring to the fxcex8 property error of the fxcex8 lens, it is possible to cancel the fxcex8 property error of the fxcex8 lens on the surface of the image-bearing member by slightly changing timings of rising-edges or falling-edges of dot clock pulses.
As a result, in the image-forming apparatus incorporating a polygon mirror in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens, with a simple circuit configuration.
(25) The clock-generating circuit described in any one of items 17, 19, 21 and 23, characterized in that the fxcex8 property error is based on a variation of refractive index of the fxcex8 lens due to an ambient temperature change.
(26) The image-forming apparatus described in any one of items 18, 20, 22 and 24, characterized in that the fxcex8 property error is based on a variation of refractive index of the fxcex8 lens due to an ambient temperature change.
According to the above invention, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens based on the variation of refractive index of the fxcex8 lens, with a simple circuit configuration.
(27) The clock-generating circuit described in any one of items 17, 19, 21 and 23, characterized in that the fxcex8 property error is a deviation from an ideal value by a design value of the fxcex8 lens.
(28) The image-forming apparatus described in any one of items 18, 20, 22 and 24, characterized in that the fxcex8 property error is a deviation from an ideal value by a design value of the fxcex8 lens.
According to the above invention, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens based on a deviation from an ideal value of a design value of the fxcex8 lens, with a simple circuit configuration.
(29) The clock-generating circuit described in any one of items 17, 19, 21 and 23, characterized in that the fxcex8 property error is based on an accuracy of a mold for manufacturing the fxcex8 lens in a molding process.
(30) The image-forming apparatus described in any one of items 18, 20, 22 and 24, characterized in that the fxcex8 property error is based on an accuracy of a mold for manufacturing the fxcex8 lens in a molding process.
According to the above invention, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by the fxcex8 property error of the fxcex8 lens based on the accuracy of the mold, with a simple circuit configuration.
(31) The clock-generating circuit described in any one of items 17, 19, 21, 23, 25, 27 and 29, characterized in that each of the sections is structured as a digital circuit in an integrated circuit.
(32) The image-forming apparatus described in any one of items 18, 20, 22, 24, 26, 28 and 30, characterized in that each of the sections is structured as a digital circuit in an integrated circuit.
According to the above invention, in the image-forming apparatus incorporating a fxcex8 lens in the optical writing system, and its clock generating circuit, it becomes possible to reduce the influence to the image quality, caused by various kinds of fxcex8 property errors, with a simple configuration of digital circuits excluding any analogue circuit.